**Core Concept**
The discovery of the anopheline mosquito as the primary vector for malaria transmission marked a significant milestone in the understanding of the disease's epidemiology and control. This breakthrough led to the development of mosquito-based control measures, such as insecticide-treated bed nets and indoor residual spraying.

**Why the Correct Answer is Right**
The scientist who made this groundbreaking discovery was Sir Ronald Ross, a British physician and parasitologist. Ross's work in Calcutta (now Kolkata) and Sierra Leone revealed the life cycle of the malaria parasite, demonstrating that it is transmitted through the bite of an infected female anopheline mosquito. This discovery earned Ross the Nobel Prize in Physiology or Medicine in 1902.

**Why Each Wrong Option is Incorrect**
**Option A:** There is no notable scientist associated with the discovery of malaria transmission by anopheline mosquito by this name.
**Option B:** Louis Pasteur made significant contributions to vaccination and germ theory but is not credited with the discovery of malaria transmission.
**Option C:** Robert Koch is known for his work on bacteriology and the discovery of the bacteria responsible for anthrax and tuberculosis, but not malaria transmission.

**Clinical Pearl / High-Yield Fact**
Ross's discovery of the anopheline mosquito as the primary vector for malaria transmission highlights the importance of vector control in disease prevention and the need for continued research into the epidemiology and control of vector-borne diseases.

**Correct Answer: D. Sir Ronald Ross**